1. Field of the Invention
This invention relates to test apparatus for fluid mass flow meters and, more particularly, to test apparatus which measures accurately the mass flow of high-temperature fluid passing through the meter undergoing test.
2. Background
Coriolis mass flow meters are well known in the art and are generally described in the following U.S. Pat. Nos. Re. 31,450, dated Nov. 29, 1983 to Smith; 4,422,338 dated Dec. 27, 1983 to Smith; and 4,491,025 dated Jan. 1, 1985 to Smith et al. Such meters have been adapted to measure the total fluid mass flow therethrough and to register same as a digital readout as described in Instruction Manual 10006 18-3-87-C entitled "DRT Digital Rate Totalizer", March, 1987, Micro Motion, Inc., Boulder, CO.
The meters are accurately calibrated at the time of manufacture. It is desirable in some cases to be able to check or prove the accuracy of the meter calibration in the field and this is particularly true in the case of meters designed to measure the mass flow of high-temperature fluids where expansion and other problems can be encountered.
Apparatus for proving and/or calibrating the performance of meters is well known in the art. The simplest system is to measure the fluid passing the meter, collect the fluid in a weigh tank and weigh same. Conducted at ambient temperatures and pressures, the apparatus can be designed with so-called open loop system wherein there need be no connection between the fluid feed lines to the tank and the weigh tank itself. When the fluid being measured is at a relatively high temperature, it is desirable to couple the weigh tank to the meter with flexible conduits to minimize the effects of the connecting piping on the weight measurements and such a construction is shown in Liu, K. T., "Application of Mass Flow Meter for Allocation Measurement of Crude Oil Production", SPE, 1986. A similar teaching is to be found in U.S. Pat. No. 3,212,318 dated Oct. 19, 1965 to Lomax.
A weight tank formed as a pressure vessel is shown in U.S. Pat. No. 3,034,331 dated May 15, 1962 to Brueckner. This is used in conjunction with volatile or flammable fluids. Other types of proving systems are also known and include apparatus for proving cryogenic meters, see U.S. Pat. No. 3,958,443 dated May 25, 1986 to Berrettini. U.S. Pat. No. 3,475,949 dated Nov. 4, 1969 to Truhan discloses using a heated or cooled fluid to heat or cool gas to a predetermined temperature prior to measuring the flow of the gas.
Various other U.S. patents and literature disclose different combinations of piping and measuring techniques and include the following: U.S. Pat. No. 3,035,434 dated May 22, 1962 to St. Clair; U.S. Pat. No. 3,226,973 dated Jan. 1, 1966 to Evans et al.; U.S. Pat. No. 3,937,048 dated Feb. 10, 1976 to St. Clair et al; U.S. Pat. No. 4,027,523 dated June 7, 1977 to St. Clair; U.S. Pat. No. 4,502,318 dated Mar. 5, 1985 to Converse et al. and Hobart, H. F., "An Automated Secondary Standard for Calibrating Liquid Flow Meters", ISA ASI176233, 1976, pp. 205-209.